This invention relates to a novel process for the production of maleic anhydride by the catalyzed high temperature oxidation of unsaturated C.sub.4 -hydrocarbons.
Maleic anhydride can be produced by the oxidation of a saturated or unsaturated C.sub.4 -hydrocarbon in the presence of a suitable catalyst. The conventional methods which use vanadium-phosphorus catalysts have the disadvantage that the resultant yields of maleic anhydride are too low. See U.S. Pat. Nos. 3,474,041 and 3,618,959. In addition, vanadium-phosphorus catalysts have only a short contact lifetime since the selectivity is markedly reduced by the discharge of phosphoric acid and by the reoxidation of tetravalent vanadium. By the continuous or discontinuous metered feeding of volatile phosphorus compounds into the process gas stream, the lifetime can be only inadequately prolonged.
In U.S. Pat. No. 4,021,427, molybdenum-antimony catalysts are described as useful for the oxidation of butadiene. These catalysts are prepared by heating a slurry of the starting compounds. By the addition of a metallic component a partial reduction of the hexavalent molybdenum is to be achieved. However, processes which employ these catalysts are unsatisfactory with respect to the reproducibility of the catalyst preparation and the selectivity with respect to maleic anhydride.
It is an object of the present invention to provide a novel process for the catalyzed oxidation of unsaturated n-C.sub.4 -hydrocarbons to maleic anhydride employing a catalyst which can be prepared in a reproducible fashion, has a long lifetime, and produces maleic anhydride with very high selectivity.